Pressure-sensitive adhesives are extremely popular for use in attachment tapes. Their use allows for fast, easy attachment of product components without the use of tools, messy liquid adhesives, or mechanical fasteners. Pressure-sensitive adhesives are available with a wide variety of properties depending on the particular application, e.g. type of substrate. Acrylic-type pressure sensitive adhesives are readily available and provide a good balance of tack, shear and peel properties on a variety of substrates and at relatively low costs.
Domestic and automotive weatherstrip seals and gaskets are commonly manufactured from materials such as ethylene-propylene-diene monomer and neoprene. These compositions are characterized as low surface energy elastomers.
For many years there has existed a desire for pressure-sensitive adhesive coated polyolefin products in which the pressure-sensitive adhesive is firmly bonded to the polyolefin and remains so at elevated temperatures. Although it is comparatively easy to bond rubber-type pressure-sensitive adhesives to polyolefin substrates, the adhesive bond tends to weaken and the product to be subject to failure at temperatures at about 65° C. or higher. Although acrylic-type pressure-sensitive adhesives have superior heat-resistance, they do not normally bond effectively to polyolefin substrates. In fact, polyolefin films are frequently used as release liners for acrylic adhesives.
Various types of treatments have been attempted, in order to increase the adhesion between a polyolefin substrate and a pressure-sensitive adhesive. However, durability of the surface treatment has oftentimes been a problem. Use of a layer or coating of material which is a good substrate for the adhesive has also been attempted. However, the weak link in this system is the interface between the polyolefin and the coating.
For example, heat-activatable polyolefin adhesives, e.g., polyethylene, polypropylene, or polyallomer (an ethylene-propylene copolymer) are well known for use on polyolefin substrates. However, such adhesives do not provide the processing and application convenience of pressure-sensitive adhesives. Furthermore, such adhesives do not yield high performance on all low-energy surfaces. In particular, heat-activatable polyolefin adhesives do not provide a sufficiently permanent bond to acrylic-type pressure sensitive adhesives.
EP-B-0 679 123 relates to a composite profile having a sealing profile and an adhesive tape, wherein the adhesive tape has a flexible supporting layer, wherein an adhesive layer covered with a removable liner is applied to a first surface of the supporting layer, wherein the supporting layer is made of foam, and wherein a second surface of the supporting layer opposite the first surface is bonded with a counter surface of the sealing profile to form a composite profile, characterized in that at least the second surface of the supporting layer is melted via the application of heat at 100° C. to 400° C. and welded with the preheated counter surface of the sealing profile.
EP-A-0 384 598 describes a dual-functional adhesive tape including a layer of a heat-activatable adhesive and a layer of pressure-sensitive adhesive which is made by adhering the pressure-sensitive adhesive to a ionizing-radiation grafted primer layer coated onto the heat-activatable adhesive.
U.S. Pat. No. 4,563,388 discloses an adhesive product comprising a polyolefin substrate and an acrylic-type pressure-sensitive adhesive which is bonded by means of a graft polymerized vinyl-coating applied on the polyolefin substrate.
Previously known dual-functional adhesive tapes incorporating heat-activatable polyolefin layer and an intermediate layer have been found to be prone to stiffness caused by the selection of the polyolefin layer. Stiffness of the polyolefin heat-activated layer can contribute to stiffness of the overall weatherstrip construction and makes it difficult for end-users to handle. Excessive stiffness also makes the tape less conformable and thus difficult to apply to irregularly curved surfaces, particularly those encountered in automotive door sealing operations.
Moreover, the application of an additional intermediate layer is very labor and cost intensive. The use of such intermediate layers also does not yield an entirely satisfactory bond over a wide variety of conditions. Fasteners of the type described in the aforementioned patents are particularly useful in the automotive industry. Automobile interiors, however, are often subject to extreme temperature and humidity conditions, for instance when a closed automobile remains in the sun for extended periods of time and/or when humidity has been allowed to enter the inside of the car.